I have discovered and solved several problems with safe door bushings for combination locks. These bushings extend through an insulation-filled space between the inner and outer walls of a safe door and receive the spindle of a combination lock. Since the insulation material used in fire resistant safes is a concrete-type material, it fixes the bushing in place once the insulation material is poured into the space between the inner and outer walls of the safe door. The spindle within the bushing remains free to rotate, however, for operating components of the combination lock mounted inside the inner wall of the safe door. For this purpose, the inner ends of the bushing require shoulders, annular grooves, and an axial groove for assembling the components of a combination lock that include tumbler wheels, spacer washers, and snap rings. The bushings have to have thick walls to accommodate the necessary machining and still be sturdy. Thick walled tubing has been more expensive than boring and machining solid stock, which is the way these bushings have been made. The long bore hole through the center of a bushing requires considerable time on a screw machine so that safe door combination lock bushings have been fairly expensive.
Another problem with a massive steel bushing extending from the outside to the inside of a safe door is that it forms a heat conductor allowing considerable heat to flow into the interior of the safe. Moreover, if the bushing is driven inward toward the interior of the safe with a large punch and sledge hammer, it may carry the tumbler wheels with it to a position making the combination lock inoperative and allowing the door to be opened.
My invention solves all these problems with a construction that costs less than the thick walled bushings previously used. My bushing is partially formed of thin walled tubing so that it greatly reduces the heat conductive path to the interior of the safe. If my bushing is driven into the interior of the safe with a punch, it does not disable the combination lock, and the door remains securely closed. My bushing also shortens the time on a screw machine and uses less expensive materials.